The present application relates to a light irradiation method, a light irradiation device, and a fine particle analyzing apparatus. More specifically, the present application relates to a technology of irradiating a specimen in a flow channel with directional light.
An irradiation technology using directional light, such as laser light, is widely used in, for example, spectral measurement or a processing technology. Directional light has uniform wavelength and phase. Therefore, when the directional light is converged using, for example, a lens, the light can be converged at a small point, so that energy density at an irradiation point of the directional light is high.
Laser spectroscopy can be classified into, for example, linear laser spectroscopy and nonlinear laser spectroscopy. The linear laser spectroscopy that measures an absorption spectrum or an excitation spectrum also provides a high sensitivity and a high resolution compared to a related spectroscopy using a light source. The non-linear spectroscopy can provide a higher sensitivity and resolution. Examples of laser spectroscopy include laser-induced fluorescence spectroscopy, laser Raman spectroscopy, Coherent anti-Stokes Raman Scattering (CARS), polarization spectroscopy, resonance ionization spectroscopy, and photoacoustic spectroscopy. In particular, spectroscopy having a high time resolution is called picosecond spectroscopy or femtosecond spectroscopy.
For example, the laser irradiation technology is also used in flow cytometry (refer to “Cell Technology Supplementary Volume: Experiment Protocol Series, Flow Cytometry With Flexibility,” by Hiromitsu Nakauchi, Published in Aug. 31, 2006 by Shujunsha, Second Edition, pp. 12 to 13). “Flow cytometry” refers to a measurement method in which a cell (a measurement object to be measured) is sorted while it is alive, to analyze, for example, the function of the cell. The cell is caused to flow into a laminar flow, to irradiate the cell passing a flow cell with laser. Fluorescent light or scattering light, which is generated by the irradiation, is measured. In a pulse detecting system, fluorescent light or scattering light, generated when the cell traverses the laser, is detected as an electrical pulse. Then, for example, a pulse height, a pulse width, or a pulse area is analyzed to analyze, for example, the function of the cell. This makes it possible to analyze the characteristics of each living cell by detecting scattering light or fluorescent light, generated from each cell.